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Date: Fri, 18 Dec 2015 15:45:12 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Tetsuya Mukawa <mukawa@igel.co.jp>,
	"Xie, Huawei" <huawei.xie@intel.com>
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Cc: dev@dpdk.org, ann.zhuangyanying@huawei.com, yuanhan.liu@intel.com
Subject: Re: [dpdk-dev] [PATCH v5 2/3] vhost: Add VHOST PMD
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On Tue, Nov 24, 2015 at 06:00:02PM +0900, Tetsuya Mukawa wrote:
> +static uint16_t
> +eth_vhost_rx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs)
> +{
> +	struct vhost_queue *r = q;
> +	uint16_t i, nb_rx = 0;
> +
> +	if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0))
> +		return 0;
> +
> +	rte_atomic32_set(&r->while_queuing, 1);
> +
> +	if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0))
> +		goto out;

I'm not quite famililar with PMD driver yet, but as far as I know,
rte_eth_rx/tx_burst() does not provide any garantee on concurrent
dequeuing/queuing. If that's true, vhost pmd could (and should)
not do that, to keep the consistency.

On the other hand, rte_vhost_dequeue/enqueue_burst() already has
such support since the beginning: above check is redundant then.
However, FYI, Huawei has just (internally) proposed to remove
it, as he thinks that's application's duty.

So, in neither way, we should not do that.

	--yliu